Thanks Treefarmer and Mel
… the old original Lamb Foot knives are not an easy pattern to find - (I got lucky and more so as you noted in reference to the condition of this example).. many different makers in the late 1800s early 1900s etched their knives Real Lamb Foot though nobody knows which maker was the origin of that etch, and even though the pattern is still made today it still seems to be predominately British… A Wright & Son LTD still makes a fair amount of them and for some reason Lamb Foot knives appear to be more popular across the pond…
I often struggled at the beginning with the difference between a Sheeps Foot and a Lambs Foot blade while the Wharncliffe is easier to depict from those two others due to the curve of the spine starting farther back towards the tang which I think you noted as well Treefarmer… I also always had the impression the Sheep Foot blade compared to the Lamb Foot had a much steeper slope at the spine at the tip and for the most part I believe that is true. It becomes less clear when I see more modern Lamb Foot blades having a steep straight angle on the spine towards the tip – however if one really starts to explore the old Sheep Foot blades from the 1800s (apparently the Sheep Foot blade as a term was coined much earlier than the Lamb Foot and there is an example in Smith’s Key from 1816 in the Pruners Category where the knife was described in writing as a Sheep Foot)… if one really starts to search through examples of old knives from the 1800s one sees many patterns that I would term a Lambs Foot though many refer to them as Sheep Foot blades or as Peach Pruning blades (the latter are just very similar to me as a Lamb Foot as you both allude to Treefarmer and Mel)… No doubt not a lot of clarity – probably because cutlers in the 1800s were more concerned about making good tools for a purpose and not ever thinking that folks like us would ever be so obsessed with any of the related details in terms of terminology or names
However more directly to the question of the difference between the two blades- the difference in my opinion and as I have now learned became more apparent in the later 1800s when knives were etched “Real Lamb Foot” – if you look at the knife I posted and at the Lamb Foot knives that Joe (FRJ) posted in the thread just below entitled “Herbert Robinson, Sheffield” you see the spine and cutting edge are not parallel as one moves from the tang to the tip (in fact some call them a tapered blade from tang to tip) and the handles have that swayback feature - that is in direct contrast to all Sheep Foot blades which no doubt have parallel spines and cutting edges - personally I think all Sheep Foot blades having a more steep slope at the tip (despite some Lamb Foot blades being close but not the majority of them)… funny thing is for a long time those Real Lamb Foot blades looked to me like someone did not sharpen them correctly and I never realized until doing some more background research (and that was very recent) that they were technically made that way with a tapered blade…
But than the question is why did they taper them and for what purpose?? I understand from a few folks that it may give better control towards the cutting edge of the tip which allows it to have more bite and when you couple that to the swayback feature of the handle which nestles in your palm as a tool that one could do more intricate cuts compared to a Sheep Foot –for example getting finer cuts to shape wood as one example…
Maybe too much info but hope this helps as a perspective between Lamb Foot and Sheep Foot blades as I have been learning
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Others say they were used to trim the hooves of those animals ... maybe 
